Under normal operating conditions, batteries such as nickel-cadmium batteries, operate with internal pressure under an equilibrium condition which the battery housing is designed to withstand. However, under certain conditions, such as when the battery is being charged too rapidly, internal pressures inside the battery may increase to the point where the housing may rupture. Since this rupturing could create a major hazard, some types of batteries normally require a battery vent, especially batteries used in hazardous environments. Prior methods of venting batteries (cells and battery packs) have included the use of rupturable membranes which prevented the rupturing of the battery housing. Unfortunately, once the membrane would get ruptured the battery became useless since the aperture in the housing would allow water, and dust, to penetrate into the housing. Some other approaches at venting gases having included methods which allow for the resealing of the vent once the pent up gases have been released. These approaches have proved costly to implement, due to the added piece parts involved. In addition these approaches have the disadvantage of not being able to be submersed in water.
More recent developments in venting technology has seen the use of GOR-TEX.RTM. fabric (W. L. Gore & Associates Inc., Newark, Dela.) and other similar materials, covering an aperture in the battery housing, whereby gases can escape from the battery, and yet keep water from penetrating the battery housing. The benefit of using a fabric like GOR-TEX.RTM. is that a water submersible vented battery can be produced.
Referring to FIG. 1, a drawing of a prior art battery 100 is shown. Battery 100 has electrical contacts 102 located on top battery surface 110. The contacts 102, allow the battery to power an external device such as a battery powered communication device. Charging contacts 106, allow battery 100 to be placed in a battery charging device for battery recharging. A vent hole or aperture 108 allows gases which are pent up inside the battery housing 104 to be released. Battery 100 can be a battery pack having a set of energy cells inside of housing 104, or could be an individual energy cell.
FIG. 2a is a partial cross-sectional view of a prior art battery venting arrangement as shown in FIG. 1, having a vent hole 108 which is covered by a piece of GOR-TEX.RTM. fabric 202 (W. L. Gore & Associates Inc., Newark, Dela.). The fabric 202 is attached by heat staking it to the inner wall of top housing 110 thereby allowing the gases inside housing 104 to be released via aperture 108. At the same time, the fabric 202 does not allow water to penetrate into the inside of housing 104 due to the fabric's small porous openings. Air can pass through the fabric 202 due to the fact that the molecular structure of air is much smaller than that of water. By stopping water intrusion into housing 104, damage to the battery cells inside of battery 100 can be avoided.
All of the prior methods mentioned, have the disadvantage of being relatively expensive to produce, and in some cases very difficult to manufacture due to the added parts required. With the need for submersible batteries increasing, especially in portable communication device applications, a need exists for a vented battery which can also be submersible.